1. Field of the Invention
The present invention relates to an additive process illumination system obtaining a specific color light by mixing a plurality of color lights, and a liquid crystal display using such an illumination system.
2. Description of the Related Art
In recent years, flat panel displays as typified by liquid crystal TVs and plasma display panels (PDPs) have become a trend, and among them, most of mobile displays are liquid crystal displays, and precise color reproducibility is desired in the mobile displays. Moreover, as backlights for liquid crystal panels, CCFLs (Cold Cathode Fluorescent Lamps) using fluorescent tubes are mainstream; however, mercury-free light sources are environmentally desired, so light emitting diodes (LEDs) and the like hold promise as light sources replacing CCFLs.
Further, illumination systems using LEDs and the like have become commercially practical recently.
In such illumination systems using LEDs in related arts, the drive currents of the LEDs are controlled by pulse width modulation (PWM) to adjust their light emission intensities (for example, refer to Japanese Unexamined Patent Application Publication No. 2005-310996).
FIG. 20 shows the circuitry of an illumination system using LEDs controlled by PWM in a related art. An illumination system 101 includes a main power source 110, constant current power sources 110R, 110G and 110B, a light source section 111 including a red LED 111R, a green LED 111G and a blue LED 111B each of which includes a plurality of serially connected LEDs, PWM drivers 113R, 113G and 113B, switches 114R, 114G and 114B, a light receiving section 115 including a red light receiving section 115R, a green light receiving section 115G and a blue light receiving section 115B, a light receiving signal processing section 116, an A/D conversion circuit 117 and a CPU (Central Processing Unit) 118. In the illumination system 101, by power supplied from the main power source 110, constant currents I101, I102 and I103 flow from the constant current power sources 110R, 110G and 110B to the red LED 111R, the green LED 111G and the blue LED 111B, respectively, and a red light, a green light and a blue light are emitted. Moreover, such color lights are received in the light receiving section 115, and the light receiving signal processing section 116 and the A/D conversion circuit 117 perform a predetermined signal process on light receiving signals of the color lights, and on the basis of the light receiving signals, control signals are supplied from the CPU 118 to the PWM drivers 113R, 113G and 113B. Then, the on/off states of the switches 114R, 114G and 114B are controlled by the PWM drivers 113R, 113G and 113B, respectively, so the lighting periods of the red LED 111R, the green LED 111G and the blue LED 111B are individually controlled.